21660540 has 96 divisors (see below), whose sum is σ = 68027904. Its totient is φ = 5103360.

The previous prime is 21660523. The next prime is 21660559. The reversal of 21660540 is 4506612.

It is a self number, because there is not a number n which added to its sum of digits gives 21660540.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 23977 + ... + 24863.

It is an arithmetic number, because the mean of its divisors is an integer number (708624).

Almost surely, 2^21660540 is an apocalyptic number.

21660540 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21660540, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (34013952).

21660540 is an abundant number, since it is smaller than the sum of its proper divisors (46367364).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21660540 is a wasteful number, since it uses less digits than its factorization.

21660540 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 947 (or 945 counting only the distinct ones).

The product of its (nonzero) digits is 1440, while the sum is 24.

The square root of 21660540 is about 4654.0885251572. The cubic root of 21660540 is about 278.7552741533.

It can be divided in two parts, 21660 and 540, that multiplied together give a square (11696400 = 3420²).

The spelling of 21660540 in words is "twenty-one million, six hundred sixty thousand, five hundred forty".